Global warming could hurt salmon fisheries in Pacific Northwest

Global warming could hurt salmon fisheries in Pacific Northwest
mongabay.com
April 2, 2007

Global warming could cause Chinook salmon populations in Washington state to decline 20-40 percent by 2050 according to a new study published in the online early edition of the Proceedings of the National Academy of Sciences (PNAS). The researchers urge policymakers to focus on restoration of lower elevation habitats in order to reduce the expected impact of climate change on salmon populations.

Using two climate change models, particularly suited to the Pacific Northwest, a team of researchers led by James Battin of the National Oceanic and Atmospheric Administration's Northwest Fisheries Science Center projected the impact on salmon populations and their habitat in the Snohomish River Basin. They found that air higher temperatures will warm rivers and causes changes in rain and snowfall patterns, degrading key salmon habitat.

"Higher air temperatures are likely to increase water temperatures, which could be harmful to salmon during the spawning, incubation, and rearing stages of their life cycle," the authors wrote. "Warmer temperatures also lead to earlier snowmelt and to a lower proportion of precipitation falling as snow.,, [leading] to elevated winter peak flows, which scour the streambed and destroy salmon eggs," they continued. "Less snowpack results in lower flows in summer and fall, reducing the amount of available spawning habitat and further increasing water temperatures."

Chinook salmon.
Courtesy of the Pacific Northwest National Lab (PNAL)

"Higher water temperatures, lower spawning flows, and, most importantly, increased magnitude of winter peak flows are all likely to increase salmon mortality in the Snohomish River Basin and in hydrologically similar watersheds throughout the region," the continued. "The resulting stress on salmon populations is liable to make recovery targets more difficult to achieve."

Overall the researchers project a 20-40 percent decline in Chinook populations by 2050. They warn that their estimates are conservative since they don't account of for the impact of rising sea levels

The researchers say that the greatest impact of warming climate will be on watersheds at the snow line. As such, and noting that few restoration projects to date have taken into account the possible effects of climate change, they argue that habitat restoration at lower elevations is likely to be more effective that efforts at higher elevations.

The authors say these efforts could reduce projected salmon mortality to around 5 percent.

"Habitat restoration can play an important role in offsetting the effects of climate change, although our results suggest that most expected climate impacts cannot be mitigated entirely"

CITATION: James Battin, Matthew W. Wiley, Mary H. Ruckelshaus, Richard N. Palmer, Elizabeth Korb, Krista K. Bartz, and Hiroo Imaki. "Projected impacts of climate change on salmon habitat restoration". Proceedings of the National Academy of Sciences, April 3.

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